1. Field of the Invention
The present invention relates to catalysts and processes for the non-oxidative dehydrogenation of hydrocarbons in the presence of steam to corresponding more-unsaturated hydrocarbons, particularly to the production of styrene from ethylbenzene.
2. Background
Potassium oxide-modified iron oxide based catalysts have long been used to non-oxidatively dehydrogenate hydrocarbons. In addition to the potassium oxide, other metals have been used to modify these iron-based catalysts; e.g., V, Co as noted in U.S. Pat. No. 4,098,723, issued Jul. 4, 1978; Mo, Ca, Cr as noted in U.S. Pat. No. 4,467,046, issued Aug. 21, 1984; Al, Cd, Mg, Mn, Ni, U, rare earths as noted in U.S. Pat. No. 4,152,300; and Sc, Y, La, Zn, W as noted in European Patent Publication 195,252, published Jan. 1, 1991.
Various types of iron oxides have been used to prepare these dehydrogenation catalysts, including the so-called red, yellow and black forms. The yellow iron oxide is usually geothite, which is the common form of hydrated iron oxide, FeO(OH). The black form is magnetite, Fe.sub.3 O.sub.4. The red form is the anhydrous form or hematite, Fe.sub.2 O.sub.3. The red form is typically prepared by calcining the yellow form to drive off the water. This calcination of the yellow iron oxide produces red iron oxide having an acicular, or needle shape. Acicular hydrated iron oxide can also be produced by direct precipitation. U.S. Pat. No. 3,364,277, issued Jan. 16, 1968, teaches the use of yellow iron oxides to prepare dehydrogenation catalysts. U.S. Pat. No. 3,703,593, issued Nov. 21, 1972, teaches the use of mixtures of red and yellow iron oxides to prepare dehydrogenation catalysts. U.S. Pat. No. 3,904,552, issued Sep. 9, 1975, specifically teaches the use of acicular (needle) form of iron oxide (example 4) to prepare dehydrogenation catalysts.
Micaceous iron oxide is a hematite material that occurs in a tabular crystal form which can be fractured to give very thin platelets or lamellar fragments. Since its crystal structure is similar to that of mica, it has been termed "micaceous". It has been used in the preparation of protective paints. See for example Bishop, "Micaceous Iron Oxide Pigments", J. Oil Col. Chem. Assoc., Transactions and Communication, 64, 57-74, 1981. It has now been found that the use of a micaceous iron oxide in the preparation of potassium oxide-modified iron oxide dehydrogenation catalysts results in catalysts with enhanced selectivities.